Launch vehicles used for space exploration use a large amount of liquid propellant while traveling through the earth's atmosphere and into outer space. Unlike long distance travel for many airplanes, there are no refueling stops or rendezvous with refueling aircraft in mid-flight for space vehicles. Therefore, launch vehicles used for space exploration must carry onboard all fuel necessary for propulsion and power generation for the entire voyage. This requirement means that launch vehicles must be equipped to store hundreds of thousands of pounds of liquid propellant, like liquid oxygen, and handle such propellant efficiently and safely.
One problem encountered with transporting large volumes of liquid fluids in launch vehicles is the sloshing of the fluids in the tanks. Slosh is caused by tank motions during travel and results in the production of forces that can affect launch vehicle stability and control. If the fluid is allowed to slosh freely in the tank, the moving fluid can have an adverse effect on the flight of the launch vehicle. For example, exciting the fluid above its natural frequency can result in oscillating, pendulum-like forces that can change the stability of the overall dynamic system of the vehicle. As is readily appreciated by those skilled in the art, sloshing fluids can produce forces that cause additional vehicle accelerations that, when responded to by the vehicle control system, form a closed loop that can lead to instability and, ultimately, structural failure. Consequently, the slosh must be suppressed.
Slosh suppression devices typically are used to damp liquid motions in the tanks of launch vehicles. Existing systems for slosh suppression primarily consist of a series of annular ring baffles arranged around the inner wall of the tank. These ring baffles run continuously around the periphery of the inside of the tank and are spaced apart by a given distance. The ring baffles are designed to not flex or bend with the moving fluid.
Numerous experiments have been performed on the effectiveness of various baffle designs. For example, NASA Technical Note D-694, dated February 1961, briefly discusses experiments involving the damping characteristics of semi-circular plates placed at given intervals around the inside of a tank. The technical note illustrates numerous different configurations for baffles that were tested. However, the experiments were aimed at gauging the effectiveness of the various baffle designs when incorporated with annular rings. The note finds that flat rings with a sharp edge are the most effective dampers for baffle depths greater than two chords.
Additionally, NASA Space Vehicle Design Criteria Report on Slosh Suppression SP-803, dated May 1969, and David G. Stephens article entitled "Flexible Baffles for Slosh Damping," J. Spacecraft (1965), discuss the use of flexible baffles to damp slosh in a tank. Both references conclude that flexible ring baffles could be used on space vehicles. However, as the Stephens article points out, a simple flat ring baffle was found to be the best damper of those tested. Although many different baffle designs have been experimented with in the past, including flexible baffles, the baffles adapted for actual use in launch vehicles continue to primarily consist of the rigid annular ring type design.
Rigid annular ring baffles have been successfully used to suppress slosh in the tank of a launch vehicle. However, ring baffles of this type add more than an insignificant amount of weight to the overall weight of the vehicle. For example, the Delta III rocket employs a rigid ring design that weighs approximately 400 pounds. In order to prevent the rocket from being unduly heavy, the weight devoted to the rigid ring design disadvantageously limits the weight of other items onboard the launch vehicles, such as the payload, the fuel and any other equipment.